The easiest way to think of it is a halfway house between fixed and static. You get the benefits of static (maximising vertical screen space) while keeping the

The easiest way to think of it is a halfway house between fixed and static. You get the benefits of static (maximising vertical screen space) while keeping the benefits of a fixed header (primary navigation always close to hand). Edit: it's not a joke, it's an established pattern found on both iOS and Android. Slightly interesting backstory with android: this effect was originally added to the stock browser on android 3.0. I loved how the tiny enhancement gave me more screen real estate, so I decided to build a JS lib to emulate the effect. The pattern didn't make it into the original chrome for Android, but after I mentioned it to Paul Irish he made it happen there too :)